Radio network node, user equipment and methods for enabling access to a radio network

ABSTRACT

Embodiments herein relate to a method in a radio network node ( 1 ) for enabling a user equipment ( 10 ) to access a radio communications network. The user equipment ( 10 ) is located in an area of the radio communications network. The radio network node ( 1 ) retrieves a system signature. The system signature is indicating a set of system information to be used by the user equipment ( 10 ) to access the radio network node ( 1 ). The radio network node ( 1 ) then transmits the system signature within the area. This enables the user equipment ( 10 ) to access the radio communications network.

TECHNICAL FIELD

Embodiments herein relate to a radio network node, a user equipment, andmethods therein. In particular, embodiments herein relate to enable theuser equipment to access a radio communication network.

BACKGROUND

In today's radio communications networks a number of differenttechnologies are used, such as Long Term Evolution (LTE), LTE-Advanced,3rd Generation Partnership Project (3GPP) Wideband Code DivisionMultiple Access (WCDMA), Global System for Mobilecommunications/Enhanced Data rate for GSM Evolution (GSM/EDGE),Worldwide Interoperability for Microwave Access (WiMax), or Ultra MobileBroadband (UMB), just to mention a few possible implementations. A radiocommunications network comprises radio network nodes providing radiocoverage over at least one respective geographical area forming a cell.The cell definition may also incorporate frequency bands used fortransmissions, which means that two different cells may cover the samegeographical area but using different frequency bands. User equipments(UE) are served in the cells by the respective radio network node andare communicating with respective radio network node. The userequipments transmit data over an air or radio interface to the radionetwork nodes in uplink (UL) transmissions and the radio network nodestransmit data over an air or radio interface to the user equipments indownlink (DL) transmissions.

Traditional radio communications networks broadcast cell-specificreference signals and system information. These signals let userequipments determine which cell the user equipments should connect toand provide information to the user equipments how they should accessthose cells. Radio network nodes that are adjacent or close to eachother need to transmit different reference signals, so that the userequipments can distinguish between them, and determine which cell orcells the user equipments should connect to.

In particular, the broadcasted system information comprises parametersthat control the timing, frequency, transmission formats, and power usedby the user equipment for initial (random access) transmissions to thenetwork. Such information may be different in different cells, e.g. tobe able to distinguish between accesses made in different cells, or toadjust the initial user equipment transmission power levels so as to fitthe characteristics of different cells. The user equipment typicallydetermines its initial transmission power using a standardized formulathat comprises as a part the received power of the cell-specificreference signal as measured by the user equipment, and may alsocomprise one or more parameters that are related to the transmissionpower of the radio network node. In this way, the transmission power ofthe signal initially transmitted by a user equipment performing randomaccess is adjusted such that it is likely received by a selected radionetwork node with a desired level: high enough for the signal to bedetectable, but not so high that the signal interferes too much withother signals in the radio communications network.

Since the radio communications network, i.e. the radio network node,does not know the location or presence of the user equipments, thecell-specific signals are transmitted with constant and relatively highpower and high periodicity. This is to ensure that all user equipmentscan read these signals at all times.

Future radio communications networks will be denser, having more accessnodes than today's network nodes. In some scenarios, the number ofaccess nodes may be considerably larger than the number of userequipments. These nodes may be more coordinated than traditional cells,for instance they may be implemented as remote radio heads, connectedwith a high bit-rate backhaul link to a network node in the corenetwork.

With dense radio communications networks, it would be very costly tobroadcast different reference signals and system information from eachradio network node, also referred to as access node, because of thelarge number of radio network nodes. Further, at any time instant, mostof these radio network nodes would not have any user equipments, thusmaking such transmissions unnecessary in practice. Also, a moving userequipment may move between access nodes more often, compared totraditional cells, making it more cumbersome for the user equipment totrack the reference signals and read the system information from eachaccess node.

The energy consumption of a radio communications network with a muchdenser deployment than today would become unacceptably high if all radionetwork nodes where to transmit individual system information. Also, theinterference level would always be rather high in such a radiocommunications network due to system information pollution and hence,even at very low traffic the Signal to Noise plus Interference Ratio(SINR) will never become really high.

The obvious solution is then to conclude that individual radio networknodes in a future dense or a super-dense deployment should not transmitindividual system information. The problem that arises then is that theuser equipment will not be able to obtain information on how to accessthe system. One problem is the uplink power setting, as indicated inFIG. 1, where high power is required to reach a radio network node A,medium power is required to reach a radio network node B, and low poweris required to reach a radio network node C. Even if it is assumed thatit can be afforded to transmit some low duty-cycle downlink referencesignal from each radio network node for the user equipment to measureon, the user equipment will not have any information on the power thatthe reference signals are transmitted with. Without knowing thetransmitted power the user equipment cannot estimate the path-loss toeach respective radio network node and hence it cannot perform aninitial access transmission with an appropriate power level. The powerlevel is only one problem that the user equipment cannot solve. Withoutsystem information the user equipment cannot determine the uplinkfrequency band to use, which pre-amble to use to access the radiocommunications network, how to handle Random Access Channel (RACH)congestion, etc.

It is worth noting that it is not always a problem if the user equipmenttransmits with unnecessarily high power when accessing a nearby radionetwork node. In a first scenario, illustrated in the left part of FIG.2, a user equipment that is positioned close to a micro radio networknode is transmitting with high power, calculated to be sufficient toreach a macro radio network node located far away. In case there is noactive transmission in the micro cell then no on-going communicationsgets disturbed by this interference. In another scenario, illustrated inthe right part of FIG. 2, however there is an on-going uplinktransmission between the micro radio network node and another userequipment. In this case the on-going communication could be severelyinterfered in case a user equipment performs an initial access with fartoo high transmission power.

Thus, transmitting system information from each radio network node, asdone today in state-of-the-art, is not energy efficient for densedeployments. Furthermore, the resulting interference from pilotpollution and system information pollution reduce SINR when load is low.

SUMMARY

An object of embodiments herein is to provide an efficient solution thatenables user equipment to communicate within the radio communicationsnetwork.

According to an aspect the object may be achieved by a method in a radionetwork node for enabling a user equipment to access a radiocommunications network. The user equipment is located in an area of theradio communications network. The radio network node retrieves a systemsignature. The system signature is indicating a set of systeminformation to be used by the user equipment to access the radio networknode. The radio network node then transmits the system signature withinthe area. This enables the user equipment to access the radiocommunications network.

According to another aspect the object is achieved by a method in theuser equipment for requesting access to the radio communications networkvia the radio network node. The user equipment receives a systemsignature from the radio network node. As stated above, the systemsignature is indicating the set of system information to be used toaccess the radio network node. The user equipment retrieves the set ofsystem information stored at the user equipment based on the receivedsystem signature. Furthermore, the user equipment requests access to theradio communications network via the radio network node using theretrieved set of system information.

According to yet another aspect the object is achieved by a radionetwork node adapted to enable a user equipment to access the radiocommunications network. The user equipment is located in an area of theradio communications network. The radio network node comprises aretrieving circuit configured to retrieve the system signature. Thesystem signature is indicating the set of system information to be usedby the user equipment to access the radio network node. Furthermore, theradio network node comprises a transmitter configured to transmit thesystem signature within the area thereby enabling the user equipment toaccess the radio communications network.

According to still another aspect the object is achieved by a userequipment adapted to request access to the radio communications networkvia the radio network node. The user equipment comprises a receiverconfigured to receive the system signature from the radio network node.The system signature is indicating the set of system information to beused to access the radio network node. The user equipment furthercomprises a retrieving circuit configured to retrieve the set of systeminformation stored at the user equipment based on the received systemsignature. Additinoally, the user equipment comprises a requestingcircuit configured to request access to the radio communications networkvia the radio network node by using the retrieved set of systeminformation.

This means that e.g. two adjacent radio network nodes may have the samesystem signature, which enables user equipments to communicate with theradio communications network in a signaling efficient manner. The amountof system information transmitted within the area is reduced, therebyhandling system information within the radio communications network inan energy efficient manner.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described in more detail in relation to theenclosed drawings, in which:

FIG. 1 is a schematic overview depicting a radio communications network,

FIG. 2 is a schematic overview depicting different situations in a radiocommunications network,

FIG. 3 is a schematic overview depicting a radio communications networkaccording to embodiments herein,

FIG. 4 is a combined flowchart and signalling scheme in a radiocommunications network according to embodiments herein,

FIG. 5 is a block diagram depicting system information according toembodiments herein,

FIG. 6 is a schematic table disclosing a mapping between systemsignatures and access information according to embodiments herein,

FIG. 7 is a schematic overview depicting a radio communications networkaccording to embodiments herein,

FIG. 8 is a schematic overview depicting a radio communications networkaccording to embodiments herein,

FIG. 9 is a schematic overview depicting a possible signal design of thesystem signatures and how different system signatures are used in nodeswith different transmission power,

FIG. 10 is a schematic flowchart depicting a method in a radio networknode according to embodiments herein,

FIG. 11 is a schematic flowchart depicting a method in a user equipmentaccording to embodiments herein,

FIG. 12 is a block diagram depicting a radio network node according toembodiments herein, and

FIG. 13 is block diagram depicting a user equipment according toembodiments herein.

DETAILED DESCRIPTION

FIG. 3 is a schematic overview of a radio communications network using atechnology, such as LTE, LTE-Advanced, WCDMA, GSM/EDGE, WiMax, UMB, justto mention a few possible implementations. The radio communicationsnetwork comprises radio network nodes 1, indicated with the dashed linesand exemplified in this example as a first macro radio network node 12,and a second macro radio network node 13, being radio network nodes of afirst type of radio network node, providing radio coverage over at leastone respective geographical area. Furthermore, the radio communicationsnetwork comprises a number of radio network nodes of a second type ofradio network node, exemplified as a first 14, second 15, third 16 andfourth 17 micro radio network nodes, covering areas within the area ofthe first macro radio network node 12. A user equipment 10 is served bythe micro radio network node 16 but also by the first macro radionetwork node 12. It should be understood by the skilled in the art that“user equipment” is a non-limiting term which means any wirelessterminal, device or node e.g. Personal Digital Assistant (PDA), laptop,mobile, sensor, relay, mobile tablets or even a small base stationcommunicating within respective cell. The respective radio network node12-17 may also be exemplified as e.g. a radio base station, a beaconnode, an access node, a relay node, a NodeB, a radio network controlled,an evolved Node B (eNB, eNode B), a base transceiver station, an AccessPoint Base Station, a base station router, or any other network unitcapable to communicate with a user equipment depending e.g. of the radioaccess technology and terminology used. The first and second types ofradio network nodes may be differentiated by downlink transmissionpower, i.e. size of coverage area. As another example, the first type ofradio network node may comprise micro radio network nodes, and thesecond type of radio network node may comprise pico radio network nodesor just remote radio heads.

A new type of signal is introduced, here called “system signature” (SS).Each access node, e.g. each radio network node 12-17, is assigned onesuch system signature, but the same system signature may be transmittedby many radio network nodes, preferably in a time-aligned fashion, as ina single frequency network manner, including those that are close andadjacent, see the example in FIG. 3, where the radio network nodes 1transmits system signatures. The system signature is designed towithstand high time dispersion, e.g. by using an extended cyclic prefix,so that the user equipment 10 may easily and reliably detect it even ifthe same signal is transmitted from different radio network nodes. Inthe example in FIG. 3, the macro radio network nodes 12,13 transmit asystem signature number 3 while micro radio network nodes 14-17 transmitsystem signature number 15. A system signature may have the followingproperties: It is locally non-unique; several radio network nodes maytransmit the same signature; it may be transmitted in broadcast SingleFrequency Network (SFN) format, i.e. with an extended cyclic prefix. Thesame system signatures transmitted from multiple radio network nodes aresuperposed over the air; it is designed for a large DiscontinuousTransmission (DTX) ratio, (e.g. 1:1000, in order to allow for low energyconsumption in each radio network node; and radio network nodes withdifferent downlink power may preferably use different system signatures.

The user equipment 10 comprises information of a mapping from systemsignature to an access related part of a system information, referred toherein as a set of system information. This mapping may be provided bytraditional broadcasting e.g. by a sparsely deployed macro layer, suchas from radio network nodes of the first type or by a selected sub-setof radio network nodes of the second type. Additionally oralternatively, the mapping may also be assumed to be known a-priori inthe user equipment 10 and may have been received in an earlier event.E.g. the mapping may be hard coded on a Subscriber Identity Module (SIM)card, or explicitly defined in a standard, or provided together with theuser equipment firmware or operating system software of the userequipment 10.

The user equipment 10 searches for and detects such system signatures inreceived signals and maps system signatures to pre-defined sets ofsystem information such as random access aspects of system information,e.g. RACH timing, RACH pre-amble, RACH initial power, RACH contentionbehaviour, etc. Thus, the user equipment 10 associates the detectedsystem signature, which is a signature sequence, with access informationvalid at a corresponding location. For example, the user equipment 10receives the system signature number 3 and maps this to a first RACHtransmission power, and when the user equipment 10 receives the systemsignature number 15 the user equipment 10 may use a second RACHtransmission power being e.g. higher than the first RACH transmissionpower.

An access procedure may be selected based on received power of systemsignature in combination with the associated set of system information,e.g. the user equipment 10 uses the received power of the signalcarrying the signature sequence combined with a known sequence specificoffset to determine initial uplink transmission power of the systemsignature.

There are several advantages with having the same system signature inmany radio network nodes. One is the reduced bandwidth requirementssince the signals occupy the same frequency spectrum. Another is thereduced power requirements since the signals are combined. Anotheradvantage is the reduced need for the user equipment 10 to monitor manydifferent signals simultaneously. The network energy efficiency isimproved since not all radio network nodes need to transmit their ownsystem information. Embodiments herein also reduce the need for manualplanning, e.g. no need to avoid Physical Cell Identity (PCI) conflictsas in current radio communications networks.

FIG. 4 is a schematic combined flowchart and signalling scheme in theradio communications network. The radio network node 1 is exemplified inthis example as the first macro radio network node 12 with reference toFIG. 3. The actions may be taken in any suitable order.

Action 401. The first macro radio network node 12 transmits a systemsignature to the user equipment 10. This system signature may bebroadcasted. The system signature may be configured from an Operationand Maintenance node. The system signature is indicating the set ofsystem information to be used by the user equipment 10 to access theradio network node 12. Thus, the system signature is associated with theset of system information. Furthermore, in some embodiments, the systemsignature may be associated with a type of radio network node. That is,the system signature may be associated to a radio network node with acertain downlink transmission power e.g. between an upper and a lowerthreshold value, above a threshold value, or below a threshold value ofthe downlink transmission power.

Action 402. The user equipment 10 retrieves system informationassociated to access the first macro radio network node 12, which systeminformation is stored at the user equipment in relation to the systemsignature. For example, the system signature, e.g. an index, is definingrandom access parameters in a table or similar.

Action 403. The user equipment 10 selects how to access the radiocommunications network, in case of receiving a plurality is signalscarrying system signatures, by selecting a system signature based onmeasured signal strengths of the signals of received system signaturesand the system information associated to the system signature. Forexample, the user equipment 10 may take the transmission power from theset of system information of the different system signatures intoaccount when selecting the system signature.

Action 404. The user equipment 10 then uses some of the set of systeminformation associated to the selected system signature to access thefirst macro radio network node 12 when transmitting an access request tothe first macro radio network node 12.

Action 405. The first macro radio network node 12 then performs anaccess procedure for the user equipment 10 in cooperation with the userequipment 10, e.g. a common RACH procedure, and wherein the first macroradio network node 12 may send an accept of the access request or a denyof the access request.

Action 406. In some embodiments the first macro radio network node 12transmits further system information over the connection established tothe user equipment 10. This action is further described in FIG. 5 below.

FIG. 5 is a block diagram depicting system information according toembodiments herein. Each system signature is associated with the set ofsystem information, may also be referred to as system informationparameters for requesting access to the radio communications network.The radio communications network may have several such systemsignatures, each system signature associated with its own set of systeminformation. Typically, a first part of the system information isspecific for each system signature. The set of system informationassociated with each system signature is transmitted or broadcasted suchthat all user equipments have a possibility to receive it, or it isassumed to be known by the user equipment 10 by some other means, e.g.stored at the user equipment 10. The broadcasted system informationcomprises a list of used physical system signatures along with thespecific system information for each system signature, such as a table.The set of system information includes information on how the userequipment 10 is to perform an initial access to the radio network node1. The system information may further be divided into Common SystemInformation (CSI) that is relevant for every radio network node in theradio communications network, such as default values of e.g. handoverparameters; and Node Specific System Information (NSSI), specific systeminformation for short, that is relevant in a specific radio network nodeonly, such as transmission capability e.g. number of antennas orsimilar. A small part of the system information is related to initialaccess, denoted as Access Information (Al) in the FIG. 5 or as the setof system information in the other figures. Al may comprise RACHinformation such as transmission power, contention, physical resource,or response channel, access restrictions such as Public Land MobileNetwork Identities PLMN id or Closed Subscriber Group (CSG), or Routingarea.

It should be noted that in order to access the radio network node 1 theuser equipment 10 needs only a small part of the system information,i.e. the part denoted Al in FIG. 5. The remaining system information maybe already known by the user equipment 10 or it may be communicatedafter the initial access is completed and a connection is establishedbetween the user equipment 10 and e.g. the third micro radio networknode 16. For example, the radio network node 1 being exemplified as thefirst macro radio network node 12 may periodically transmit the Al tothe user equipment 10. The third micro radio network node 16 maytransmit NSSI after initial node access, also referred to as access at afirst time, and CSI may be transmitted after initial system access e.g.upon request, also referred to as access at a first time.

An example outlining the some of the content of a pre-defined table thatmaps system signature to access information is shown in FIG. 6, which isa pre-defined table that the user equipment 10 uses to map a detectedsystem signature to Al, that is the set of system information associatedto the system signature. In a first colon System signature Index (SSindex) is defined. A Valid DL band is defined in a second colon. In athird colon RACH uplink band index is defined. RACH P₀ power offset isdefined in the fourth colon. RACH pre-amble root sequence is defined ina last colon. From FIG. 6 it is disclosed that e.g. the SS2 indicates avalid DL band of 1.8-1.9 GHz, the RACH UL band index is 155, RACH poweroffset is and the 6 dB, and the RACH pre-amble root sequence is 68.

FIG. 7 is a schematic overview depicting a radio communications networkaccording to some embodiments. It is assumed that each user equipment 10reads and stores at least the initial access related part of the systeminformation for each system signature. The user equipment 10 then triesto detect any received system signatures and measures the receivedstrength of them. In case multiple radio network nodes transmit the samesystem signature, the user equipment 10 will measure the combinedstrength of the signals received. Before making an initial transmission,the user equipment 10 selects one system signature, based on thereceived strengths and system information parameters. In the simplestcase the user equipment 10 may select the strongest system signature.More realistically, the radio communications network may provide anoffset, also referred to as a signature-specific power offset, that theuser equipment 10 may add to the received signal strength, and then takethe system signature with the highest resulting value. Typically thisoffset only accounts for a difference in transmit power between radionetwork nodes of different types. But an offset may also be used forother purposes such as load-balancing between different deploymentlayers, that is, different types of radio network nodes, in the network.E.g. by giving micro radio network nodes an increased offset thelikelihood that the user equipments 10 will select a micro radio networknode, which e.g. off-loads the macro radio network nodes will increase.The user equipment 10 then uses the system information associated withthe selected system signature when performing the initial access.

In the example of FIG. 7, the user equipment 10 has stored knowledgethat a radio network node 1, being exemplified as the first macro radiobase station 12, with SS₃ transmits with a transmission power P_(TX)=50dBm and another radio network node 1, being exemplified as the thirdmicro radio base station 16, with SS₁₅ transmits with a transmissionpower P_(TX)=30 dBm. The user equipment 10 then receives a signalcarrying the SS₃ with a reception power P_(RX)=−30 dBm, and a signalcarrying the SS₁₅ with a reception power P_(RX)=−30 dBm. Thus, apathloss between the first macro radio network node 12 and the userequipment 10 is 50 dBm—(−30 dBm)→80 dB and a pathloss from the thirdmicro radio network node 16 to the user equipment 10 is 30 dBm—(40dBm)→70 dB. The user equipment 10 then selects system signature SS₁₅andthereby access parameter associated with SS₁₅ stored in the userequipment 10 based on the pathloss. Thus, using a-priori knowledge ofthe transmitted power of each system signature, the user equipment 10selects in the example, access parameters corresponding to the systemsignature received with less power.

The third micro radio network node 16 monitors a received radio signalin an uplink band and listens for user equipment transmissions atpre-defined time slots all defined in the access information associatedto the SS₁₅.

At any given time, the third micro radio network node 16 may or may nottransmit its system signature. For instance, when the third micro radionetwork node 16 has not received any user equipment transmissions forsome time, the third micro radio network node 16 may stop transmittingits system signature. As soon as the third micro radio network node 16receives any user equipment transmissions, the third micro radio networknode 16 may then start to transmit its system signature again. The thirdmicro radio network node 16 may also start to transmit signaturesequence when the third micro radio network node 16 needs to protect theuplink frequency band from high interference from user equipmentsperforming initial access, see FIG. 8.

In FIG. 8 the radio network node 1, exemplified as the first micro radionetwork node 14, may determine not to transmit a system signature if asystem signature is provided by other nodes anyway e.g. a macro systemsignature from the first macro radio network node 12, and there are noon-going UL transmissions to protect from access interference. The firstmacro radio network node 12 may be ensuring that the area is covered byat least one system signature. The other radio network nodes 15-17serving user equipments 10,101,102 transmit their respective systemsignature since these other radio network nodes 15-17 protect UL frominterference.

As stated above radio network nodes 1 with significantly differenttransmission power, e.g. first and second type exemplified herein, mayneed to have different system information, and should therefore havedifferent system signatures. Thus, different types of radio networknodes may have different system signatures. For instance, the radionetwork nodes 1 in the radio communications network may be partitionedinto different power classes, each class having its own systemsignature. All radio network nodes 1 in the same class would then havethe same signature, unless the radio network nodes 1 need differentsystem information for other reasons, e.g. backhaul capabilities,processing capabilities or similar. The different types may also beclassified based on activity level, e.g. radio network nodes 1 being inactive mode or in sleep mode.

The system information associated with all system signatures istypically broadcasted by one or more radio network nodes 1, in SingleFrequency Network (SFN) style, such as Orthogonal Frequency DivisionMultiplexing (OFDM) with extended cyclic prefix. For instance it may bebroadcasted by only a few high-power radio network nodes 1. It may alsobe stored in the user equipments 10,101,102 and not transmitted at all.

The system signature may be compared to a cell-specific reference signal(CRS). Similar to the CRS, the system signature is associated with asystem information, and controls the initial user equipmenttransmissions. One important difference is that many radio networknodes, even adjacent, may have the same system signature, as long asthey have similar transmission power or activity. In fact, all radionetwork nodes of the same type in the whole radio communications networkmay have the same system signature. In current systems a Physical CellIdentity (PCI) conflict would occur in case two neighboring radionetwork nodes would have the same PCI and hence transmit the same CRS.Another difference is that the actual system information is notnecessarily transmitted from the radio network node that transmits thesystem signature but from another radio network node.

Furthermore, in current radio communications networks the resources inthe cells typically have very low utilization. Even if there are cellsin the radio communications network that occasionally experience highload, an average cell is idle most of the time. In e.g. LTE networks atypical cell transmits data in only 1% of all sub-frames, even ifpredictions on future traffic growth are taken into account this numberstays well below 5% for an average base station. This value, singledigit per cent, may be used as guidance when designing a new systemsignature. In some embodiments the system signature allows for as muchDiscontinuous Transmission (DTX) as possible, being transmitted with aperiodicity below a threshold indicating high DTX. But if an averageradio network node need to be active during around 1% of the time inorder to transmit data then it is sufficient if the system signature hasa DTX ratio that is in that order or lower.

In FIG. 9 an example of the current LTE standard is shown as areference. If one OFDM symbol in a subframe (marked black), of a radioframe of 10 ms is set aside every super frame ‘T_(superframe)’ of e.g.100 ms, a system signature physical signal with the desired propertiesis obtained. The subframe may be e.g. an Multicast/Broadcast over aSingle Frequency Network (MBSFN) like subframe of 1 ms. In FIG. 9 it isalso shown how radio network nodes 1, indicated with the dashed lines,with different transmit power use different system signatures: e.g. ahorizontal striped symbol is allocated to a macro radio network node,e.g. the first macro radio network node 12; a wavy striped symbol isallocated to the second type of radio network node, e.g. the first microradio network node 16; and a diagonally striped symbol is allocated to athird type of radio network node e.g. first and second pico radionetwork nodes 21, 22. Thereby, different radio network nodes useddifferent system signatures or sequences respectively. The sub frame maybe a MBSFN subframe with 10 symbols and an extended cyclic prefix (CP),indicated by the dotted symbols. By using the same system signature intwo adjacent areas or cells it is ensured that the signals add in aconstructive manner instead of in an interfering manner. Comparing withordinary CRS, it is enabled to either transmit the system signature withless power, which reduces network energy consumption, or larger cells inthe macro layer deployment may be used. Larger cells in the macro layeralso increase the support for radio network node sleep mode in theunderlying network layers. For each active node there may be a largernumber of in-active nodes if the macro layer is sparse. If two adjacentnodes are transmitting the same CRS in current systems then perdefinition they will form a joint cell. Since for a joint cell they mustalso transmit exactly the same synchronization signals and systembroadcast signals. Also all CRS-based control and data channels must betransmitted in identical manner from both nodes. If they fail to do anyof this then a PCI-conflict appears and that is something that is notallowed to happen during normal operation. This is an error event thatwill cause dropped calls and handover failures and it must be resolved.With system signature this is allowed since the user equipment 10 doesnot assume that any single node transmits the system signature. The userequipment 10 may be assigned a cell after the initial access has beenperformed. In the access procedure the user equipment 10 will receiveinformation that enable it to access a cell. The cell might not havebeen there prior to the initial access of the user equipment 10.

The method actions in the radio network node 1, exemplified above asradio network nodes 12-17 and 21,22, for enabling the user equipment 10to access the radio communications network according to some generalembodiments will now be described with reference to a flowchart depictedin FIG. 10. The user equipment 10 is localized in an area of the radiocommunications network. The actions do not have to be taken in the orderstated below, but may be taken in any suitable order. Actions performedonly in some embodiments are illustrated with dashed boxes.

Action 1001. The radio network node 12 retrieves the system signature.As stated above the system signature is indicating the set of systeminformation to be used by the user equipment 10 to access the radionetwork node 12 and thereby also the radio communications network as theradio network node 12 is comprised in the radio communications network.This may be retrieved from within the radio network node 12 or from anoperation and management system during configuration. Furthermore, thesystem signature may be manually inserted when setting up the radio basestation 12 or during manufacturing.

In some embodiments the radio network node 12 is of a type of radionetwork node out of a plurality of types of radio network nodes and thesystem signature is associated to the type of the radio network node 12.The type of the radio network node 12 may be defined by a downlinktransmission power of the radio network node 12 and/or by an activitylevel of the radio network node 12. E.g. the type may be defined by aninterval of the downlink transmission power of the radio network node 12indicating the size of the area covered by the radio network node 12.The type may additionally or alternatively be defined by an interval ofthe activity level of the radio network node 12, e.g. sleeping mode oractive mode.

In some embodiments the system signature comprises an extended cyclicprefix and the system signature may be transmitted in a timesynchronised manner within the radio communications network e.g. in asingle frequency network manner.

In some embodiments the set of system information indicated by thesystem signature comprises information of at least one parameter relatedto a random access configuration.

Action 1002. In some embodiments the radio network node 12 broadcaststhe set of system information to be used to access the radio networknode 12, and an indication or association that the system signature isindicating the set of system information with a pre-set periodicity.Thus, the radio network node 12 may broadcast a table indicating arelation between different system signatures and sets of systeminformation. The pre-set periodicity may be set so that resources areused in an efficient manner, e.g. transmitted every third super frame orsimilar. The radio network node 12 may receive instructions to broadcastthe set of system information from an operation and maintenance systemor similar during configuration. Only some of radio network nodes in theradio communications network may be instructed to broadcast the set ofsystem information.

Action 1003. The radio network node 12 transmits the system signaturewithin the area thereby enabling the user equipment 10 to access theradio communications network. The system signature may be transmittedwith a periodicity below a periodicity threshold. Thus, a long DTX maybe achieved reducing used resources and interference. The periodicitythreshold may be set lower than a periodicity of common systeminformation as standardised.

Action 1004. The radio network node 12 may in some embodiments detect alevel of communication activity within the radio network node 12. Theperiodicity of the transmitting the system signature may then be basedon the detected level of communication activity. Communications activitymay relate to either uplink communication, downlink communication orboth. In some embodiments the periodicity is to zero when the detectedlevel of communications activity in uplink is below an activitythreshold, e.g. when the communication activity in the uplink is zeroover a period of time indicating no traffic within the area. Theperiodicity may be set to a higher value, that is, transmission occuroften, when communication in downlink is high as resources are alreadyin use.

Action 1005. The radio network node may communicate common systeminformation related to the radio communications network to the userequipment 10 when the user equipment 10 has requested access to theradio communications network for a first time. The common systeminformation is different than the set of system information used toaccess the radio network node 12.

Action 1006. In some embodiments the radio network node is communicatingspecific system information related to the radio network node 12 to theuser equipment 10 when the user equipment 10 has requested access to theradio network node 12 for a first time. The specific system informationis different than the set of system information used to access the radionetwork node 12,

The method actions in the user equipment 10 for requesting access to theradio communications network via the radio network node 1 according tosome general embodiments will now be described with reference to aflowchart depicted in FIG. 11. The actions do not have to be taken inthe order stated below, but may be taken in any suitable order. Actionsperformed only in some embodiments are illustrated with dashed boxes.

Action 1101. The user equipment 10 may receive from the radio networknode 1 or another radio network node 12-17, the set of systeminformation and the indication that the system signature is indicatingthe set of system information. This may be performed when the userequipment 10 is activated or entering a cell for the first time. The setof system information and the indication may be periodically transmittedwithin the cell.

Action 1102. The user equipment 10 may then store the receivedindication and the set of system information in the user equipment 10 tobe used when attaching or connecting to the radio communicationsnetwork.

Action 1103. The user equipment 10 receives the system signature fromthe radio network node 1. As stated herein the system signature isindicating a set of system information to be used to access the radionetwork node 1. In some embodiments the user equipment 10 furtherreceives specific system information related to the radio network node 1when the user equipment 10 has requested access to the radio networknode 1 for a first time. The specific system information is differentthan the set of system information used to access the radio network node1. In some embodiments the user equipment 10 further receives commonsystem information related to the radio communications network when theuser equipment 10 has requested access to the radio communicationsnetwork for a first time. The common system information is differentthan the set of system information used to access the radio network node1.

Action 1104. The user equipment 10 retrieves the set of systeminformation stored at the user equipment 10 based on the received systemsignature.

Action 1105. The user equipment 10 requests access to the radiocommunications network via the radio network node 1 using the retrievedset of system information.

In some embodiments the set of system information and an indicationassociating the system signature to the set of system information ispre-set at the user equipment. E.g. may be stored at a SIM card insertedin the user equipment 10, preconfigured at firmware or at OperationalSystem (OS) in the user equipment 10.

Action 1106. In some embodiments the user equipment 10 receives adifferent system signature. E.g. the user equipment may receive a signalfrom the first micro radio base station 16 carrying a different systemsignature.

Action 1107. The user equipment 10 may then select access procedurebased on signal strengths of the signals carrying the system signatures,and/or the set of system information indicated by respective systemsignature. The set of system information may indicate type of the radionetwork node.

FIG. 12 is a block diagram depicting a radio network node adapted toenable the user equipment 10 to access the radio communications networkaccording to some embodiments herein The user equipment 10 is located inan area of the radio communications network.

The radio network node 12 comprises a retrieving circuit 1201 configuredto retrieve the system signature. As stated above, the system signatureis indicating the set of system information to be used by the userequipment 10 to access the radio network node 12 and thus the radiocommunications network. The radio network node 1 may in some embodimentsherein be defined as a type of radio network node out of a plurality oftypes of radio network nodes. The system signature is then associated tothe type of the radio network node 1. As previously stated, the type ofthe radio network node 1 may be defined by the downlink transmissionpower of the radio network node 1 and/or by the activity level of theradio network node 1. The system signature may be a one or two bitindication.

The radio network node comprises a transmitter 1202 configured totransmit the system signature within the area thereby enabling the userequipment 10 to access the radio communications network. The transmitter1202 may be configured to transmit with a periodicity below aperiodicity threshold. The system signature may comprise an extendedcyclic prefix and the transmitter 1202 may be configured to transmit thesystem signature in a time synchronized manner within the radiocommunications network.

Furthermore, the radio network node 1 comprises, in some embodiments, adetecting circuit 1203 configured to detect a level of communicationactivity within the radio network node 1. The transmitter 1202 may thenbe configured to transmit with a periodicity based on the detected levelof communication activity. The periodicity may be zero when the detectedlevel of communications activity in uplink is below an activitythreshold.

The radio network node 1 may further comprise a broadcasting circuit1204 configured to broadcast the set of system information to be used toaccess the radio network node 1. The broadcasting circuit may further beconfigured to broadcast an indication, such as a table, that the systemsignature is indicating the set of system information with a pre-setperiodicity.

The radio network node 1 comprises in some embodiments a communicationcircuit 1205 configured to communicate specific system informationrelated to the radio network node 1 to the user equipment 10 when theuser equipment 10 has requested access to the radio network node 1 for afirst time. The specific system information is different than the set ofsystem information used to access the radio network node 1. Additionallyor alternatively, the communication circuit 1205 may be configured tocommunicate common system information related to the radiocommunications network to the user equipment 10 when the user equipment10 has requested access to the radio communications network for a firsttime. The common system information is different than the set of systeminformation used to access the radio network node 1.

The set of system information comprises information of at least oneparameter related to a random access configuration.

The embodiments herein for enabling access to the radio network node maybe implemented through one or more processors, such as a processingcircuit 1206 in the radio network node 1 depicted in FIG. 12, togetherwith computer program code for performing the functions and/or methodactions of the embodiments herein. The program code mentioned above mayalso be provided as a computer program product, for instance in the formof a data carrier carrying computer program code for performingembodiments herein when being loaded into the radio network node 1. Onesuch carrier may be in the form of a CD ROM disc. It is however feasiblewith other data carriers such as a memory stick. The computer programcode may furthermore be provided as pure program code on a server anddownloaded to the radio network node 1. The radio network node 1 mayfurther comprise a memory 1207 to be used to store data on, such assystem signatures, system information, applications to perform methodsherein and similar. The memory 1207 may comprise one or more memoryunits and may be used to store for example data such as thresholdvalues, quality values, user equipment context, timers, cyphering keys,application to perform the methods herein when being executed on theradio network node 1 or similar.

FIG. 13 is a block diagram depicting the user equipment 10 according tosome embodiments herein adapted to request access to the radiocommunications network via the radio network node 1.

The user equipment 10 comprises a receiver 1301 configured to receivethe system signature from the radio network node 1. As stated above, thesystem signature is associated to a set of system information to be usedto access the radio network node 1. In some embodiments the radionetwork node is of a type of radio network node out of a plurality oftypes of radio network node and the system signature is associated tothe type of radio network node. The type may be defined by downlinktransmission power of the radio base station or activity. The receiver1301 may further be configured to receive, from the radio network node 1or another radio network node 12-17, the set of system information andan indication that the system signature is indicating the set of systeminformation. The receiver 1301 may further be configured to receivespecific system information related to the radio network node 1 when theuser equipment 10 has requested access to the radio network node 1 for afirst time. The specific system information is different than the set ofsystem information used to access the radio network node 1. Additionallyor alternatively, the receiver 1301 may further be configured to receivecommon system information related to the radio communications networkwhen the user equipment 10 has requested access to the radiocommunications network for a first time. The common system informationis different than the set of system information used to access the radionetwork node 1.

The user equipment 10 further comprise a retrieving circuit 1302configured to retrieve, e.g. in response to the reception and decodingof the system signature, the set of system information stored at theuser equipment based on the received system signature. The set ofinformation may e.g. be access information stored at a memory 1303. Theuser equipment 10 may additionally be configured to store the set ofsystem information and the indication at the memory 1303 in the userequipment 10 to be used when attaching to the radio communicationsnetwork. In some embodiments the set of system information and anindication associating the system signature and the set of systeminformation, such as the table shown in FIG. 6, is pre-set at the userequipment 10.

Furthermore, the user equipment comprises a requesting circuit 1304configured to request access to the radio communications network via theradio network node 1 by using the retrieved set of system information,e.g. by transmitting an access request using a certain transmissionpower via a transmitter 1305.

In some embodiments, the receiver 1301 is further configured to receivea different system signature. Then the user equipment 10 may furthercomprise a selecting circuit 1306 configured to select an accessprocedure based on signal strengths of signals carrying the systemsignatures, and/or the set of system information indicated by respectivesystem signature.

The embodiments herein for enabling access to the radio communicationsnetwork may be implemented through one or more processors, such as aprocessing circuit 1307 in the user equipment 10 depicted in FIG. 13,together with computer program code for performing the functions and/ormethod actions of the embodiments herein. The program code mentionedabove may also be provided as a computer program product, for instancein the form of a data carrier carrying computer program code forperforming embodiments herein when being loaded into the user equipment10. One such carrier may be in the form of a CD ROM disc. It is howeverfeasible with other data carriers such as a memory stick. The computerprogram code may furthermore be provided as pure program code on aserver and downloaded to the user equipment 10. The memory 1303 maycomprise one or more memory units and may be used to store for exampledata access information, system signatures, associating information,applications to perform the methods herein when being executed on theuser equipment 10 or similar.

Those skilled in the art will also appreciate that the various“circuits” described may refer to a combination of analogue and digitalcircuits, and/or one or more processors configured with software and/orfirmware (e.g., stored in memory) that, when executed by the one or moreprocessors, perform as described above. One or more of these processors,as well as the other digital hardware, may be included in a singleapplication-specific integrated circuit (ASIC), or several processorsand various digital hardware may be distributed among several separatecomponents, whether individually packaged or assembled into asystem-on-a-chip (SoC).

In the drawings and specification, there have been disclosed exemplaryembodiments. However, many variations and modifications can be made tothese embodiments. Accordingly, although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation, the scope of the embodiments being defined bythe following claims.

1. A method in a radio network node for enabling a user equipment toaccess a radio communications network, wherein the user equipment islocated in an area of the radio communications network, the methodcomprises: retrieving a system signature, which system signature isindicating a set of system information to be used by the user equipmentto access the radio network node; and transmitting the system signaturewithin the area thereby enabling the user equipment to access the radiocommunications network.
 2. The method according to claim 1, wherein theradio network node is of a type of radio network node out of a pluralityof types of radio network nodes and the system signature is associatedto the type of the radio network node.
 3. The method according to claim2, wherein the type of the radio network node is defined by at least oneor more of a downlink transmission power of the radio network node andan activity level of the radio network node.
 4. The method according toclaim 1, wherein the transmitting is performed with a periodicity belowa periodicity threshold.
 5. The method according to claim 4, furthercomprising: detecting a level of communication activity within the radionetwork node, and wherein the periodicity of the transmitting is basedon the detected level of communication activity.
 6. The method accordingto claim 5, wherein the periodicity is zero when the detected level ofcommunications activity in uplink is below an activity threshold.
 7. Themethod according to claim 1, further comprising: broadcasting the set ofsystem information to be used to access the radio network node and anindication that the system signature is indicating the set of systeminformation with a pre-set periodicity.
 8. The method according to claim1, further comprising: communicating specific system information relatedto the radio network node, being different than the set of systeminformation used to access the radio network node, to the user equipmentwhen the user equipment has requested access to the radio network nodefor a first time.
 9. The method according to claim 1, furthercomprising: communicating common system information related to the radiocommunications network, being different than the set of systeminformation used to access the radio network node, to the user equipmentwhen the user equipment as requested access to the radio communicationsnetwork for a first time.
 10. The method according to claim 1, whereinthe system signature comprises an extended cyclic prefix.
 11. The methodaccording to claim 10, wherein the system signature is transmitted in atime synchronised manner within the radio communications network. 12.The method according to claim 1, wherein the set of system informationcomprises information of at least one parameter related to a randomaccess configuration.
 13. A method in a user equipment for requestingaccess to a radio communications network via a radio network node, themethod comprising: receiving a system signature from the radio networknode, which system signature is indicating a set of system informationto be used to access the radio network node; retrieving the set ofsystem information stored at the user equipment based on the receivedsystem signature; and requesting access to the radio communicationsnetwork via the radio network node using the retrieved set of systeminformation.
 14. The method according to claim 13, wherein the radionetwork node is of a type of radio network node out of a plurality oftypes of radio network nodes and the system signature is associated tothe type of the radio network node.
 15. The method according to claim13, further comprising: receiving, from the radio network node oranother radio network node, the set of system information and anindication that the system signature is indicating the set of systeminformation; and storing the set of system information and theindication in the user equipment to be used when attaching to the radiocommunications network.
 16. The method according to claim 13, whereinthe set of system information and an indication associating the systemsignature and the set of system information is pre-set at the userequipment.
 17. The method according to claim 13, further comprising:receiving a different system signature, and selecting an accessprocedure based on at least one or more of signal strengths of signalscarrying the system signatures and the set of system informationindicated by respective system signature.
 18. The method according toclaim 13, wherein the receiving further comprises to receive specificsystem information related to the radio network node, being differentthan the set of system information used to access the radio networknode, when the user equipment has requested access to the radio networknode for a first time.
 19. The method according to claim 13, wherein thereceiving further comprises to receive common system information relatedto the radio communications network, being different than the set ofsystem information used to access the radio network node, when the userequipment has requested access to the radio communications network for afirst time.
 20. A radio network node adapted to enable a user equipmentto access a radio communications network, wherein the user equipment islocated in an area of the radio communications network, wherein theradio network node comprises: a retrieving circuit configured toretrieve a system signature, which system signature is indicating a setof system information to be used by the user equipment to access theradio network node; and a transmitter configured to transmit the systemsignature within the area thereby enabling the user equipment to accessthe radio communications network.
 21. The radio network node accordingto claim 20, wherein the radio network node is of a type of radionetwork node out of a plurality of types of radio network nodes and thesystem signature is associated to the type of the radio network node.22. The radio network node according to claim 21, wherein the type ofthe radio network node is defined by at least one or more of a downlinktransmission power of the radio network node and an activity level ofthe radio network node.
 23. The radio network node according to claim20, wherein the transmitter is configured to transmit with a periodicitybelow a periodicity threshold.
 24. The radio network node according toclaim 23, further comprising: a detecting circuit configured to detect alevel of communication activity within the radio network node, andwherein the transmitter is configured to transmit with a periodicitybased on the detected level of communication activity.
 25. The radionetwork node according to claim 24, wherein the periodicity is zero whenthe detected level of communications activity in uplink is below anactivity threshold.
 26. The radio network node according to claim 20,further comprising: a broadcasting circuit configured to broadcast theset of system information to be used to access the radio network node,and an indication that the system signature is indicating the set ofsystem information with a pre-set periodicity.
 27. The radio networknode according to claim 20, further comprising: a communication circuitconfigured to communicate specific system information related to theradio network node, being different than the set of system informationused to access the radio network node, to the user equipment when theuser equipment has requested access to the radio network node for afirst time.
 28. The radio network node according to claim 20, furthercomprising: a communication circuit configured to communicate commonsystem information related to the radio communications network, beingdifferent than the set of system information used to access the radionetwork node, to the user equipment when the user equipment hasrequested access to the radio communications network for a first time.29. The radio network node according to claim 20, wherein the systemsignature comprises an extended cyclic prefix.
 30. The radio networknode according to claim 29, wherein the transmitter is configured totransmit the system signature in a time synchronised manner within theradio communications network.
 31. The radio network node according toclaim 20, wherein the set of system information comprises information ofat least one parameter related to a random access configuration.
 32. Auser equipment adapted to request access to a radio communicationsnetwork via a radio network node, the user equipment comprises: areceiver configured to receive a system signature from the radio networknode, which system signature is indicating a set of system informationto be used to access the radio network node; a retrieving circuitconfigured to retrieve the set of system information stored at the userequipment based on the received system signature; and a requestingcircuit configured to request access to the radio communications networkvia the radio network node by using the retrieved set of systeminformation.
 33. The user equipment according to claim 32, wherein theradio network node is of a type of radio network node out of a pluralityof types of radio network nodes and the system signature is associatedto the type of the radio network node.
 34. The user equipment accordingto claim 32, wherein the receiver is further configured to receive, fromthe radio network node or another radio network node, the set of systeminformation and an indication that the system signature is indicatingthe set of system information, and the user equipment is configured tostore the set of system information and the indication at a memory inthe user equipment to be used when attaching to the radio communicationsnetwork.
 35. The user equipment according to claim 32, wherein the setof system information and an indication between the system signature andthe set of system information is pre-set at the user equipment.
 36. Theuser equipment according to claim 32, wherein the receiver is furtherconfigured to receive a different system signature, and the userequipment further comprises: a selecting circuit configured to select anaccess procedure based on at least one or more of signal strengths ofsignals carrying the system signatures and the set of system informationindicated by respective system signature.
 37. The user equipmentaccording to claim 32, wherein the receiver is further configured toreceive specific system information related to the radio network node,being different than the set of system information used to access theradio network node, when the user equipment has requested access to theradio network node for a first time.
 38. The user equipment according toclaim 32, wherein the receiver is further configured to receive commonsystem information related to the radio communications network, beingdifferent than the set of system information used to access the radionetwork node, when the user equipment has requested access to the radiocommunications network for a first time.